344 THE WATER PROBLEM OF A LARGE CITY 



fountains for schools, railroad stations, and shops (Fig. 211). 

 Bubbling fountains are sanitary because the flowing water 



washes away germs left 

 by one person and keeps 

 the fountain clean for 

 the next drinker. 

 Many states have re- 

 quired the railroads to 

 abolish the common 

 drinking cup and to 

 substitute sanitary 

 paper cups. 



The composition of 

 water. - - Water was 

 long thought to be a 

 simple substance, but 

 toward the end of the 

 eighteenth century it 

 was found to consist of 

 two quite different sub- 

 stances, oxygen (O) and 

 hydrogen (H). 



In order to prove this, send an electric current through water. 

 Tip the ends of the wires which dip into the water with plati- 

 num and pour a little acid into the water. The acid facilitates 

 chemical action very much as oil on machinery facilitates 

 motion. As soon as the current begins to flow bubbles of gas 

 rise from the end of the wire by which the current enters the 

 water, and other bubbles of gas rise from the end of the wire 

 by which the current leaves the water. These gases have come 

 from the water and are the substances of which it is composed. 

 If we place over each end of the wire an inverted jar filled with 

 water, the gases are easily collected (Fig. 212). The first thing 



FIG. 211. A sanitary drinking fountain. 



